STRUCTURAL CHARACTERIZATION OF BRITTLE DEFORMATION IN SIERRA DE PACHUCA, CENTRAL SECTOR OF THE TRANSMEXICAN VOLCANIC BELT, MÉXICO

The Sierra de Pachuca (SP), Estado de Hidalgo, Mexico, located in the Central Sector of the Trans-Mexican Volcanic Belt (TMVB), hosts Plio-Pleistocene rhyolitic, dacitic, and andesitic rocks. The geological evolution of the SP is poorly understood in spite the fact that in this sector of the TMVB, the Pachuca-Real del Monte Mining District was formally exploited since the early nineteenth century. This mining district is, in part, a structurally controlled deposit characterized by Ag-rich quartz veins infilling faults.Digital Elevation Models reveal that the SP is crosscut by three dominant regional topographic lineaments oriented NNW-SSE, NE-SW, and WNW-ESE. Short extent, convex to the north curved lineaments are also present in the area. Traces of these lineaments have been tracked in the field in order to find associated faulted structures. The orientation of the principal stress s1, inferred from direct measurements on fault planes, suggests that at least four faulting events affected the SP. Following the right hand rule, the trend and plunge of s1 in each event is 195/15, 128/2, 307/4, and 213/3.Direction of the principal stresses in each event and fault crosscutting relations point to a thrusting event as the oldest episode, subsequently followed by three pulsating stages of extension that caused normal faulting with different direction of maximum extension. Our findings allow us to propose a brittle deformation model that can shed light into the understanding of the ore emplacement event that resulted in the Pachuca-Real del Monte Mining District. In addition, our model can be used to explain the geologic evolution of the SP in the context of the tectonic history of the Central Sector of the TMVB.